Researchers Downplay Size of Reaper IoT Botnet

The Mirai-like "Reaper" botnet that began infecting Internet of Things (IoT) devices in late September has only ensnared up to 20,000 bots so far, according to estimates from Arbor Networks.

Called Reaper, the botnet was said a couple of weeks ago to have infected over one million organizations worldwide, but Arbor claims that the actual size of the botnet fluctuates between 10,000 and 20,000 bots in total.

The botnet’s size, the researcher reveal, could change at any time. An additional 2 million hosts have been already identified by the botnet scanner as potential nodes, although they haven’t been ensnared into Reaper yet.

“At this time, it is not clear why these candidate bots have not been co-opted into the botnet. Possible explanations include: misidentification due to flaws in the scanning code, scalability/performance issues in the Reaper code injection infrastructure, or a deliberate decision by the Reaper botmasters to throttle back the propagation mechanism,” Arbor’s ASERT researchers note.

The botnet was likely created to launch distributed denial of service (DDoS) attacks and its operators are expected to offer it as a service for the intra-China DDoS-for-hire market. It can launch SYN-floods, ACK-floods, http floods, and DNS reflection/amplification attacks.

Reaper shows code similarities with Mirai, but isn’t considered a clone. While Mirai uses password cracking for infection, the new botnet exploits vulnerabilities in targeted IoT devices, Chinese security company Qihoo says.

The firm has discovered 9 vulnerability exploits integrated into the current samples, targeting devices from 7 different manufacturers, namely Dlink, Goahead, JAWS, Netgear, Vacron NVR, Linksys, and AVTECH. The exploits list is actively updated, with one targeting Vacron NVR that was added within two days after its public disclosure on October 8.

“The botnet has embedded more than 100 DNS open resolvers in its LUA sample, so DNS amplification attack can be easily carried out. About one-third of these open DNS servers have been used as reflector in real DNS amplification attacks. We have yet to see this type of config in any other Mirai variants,” Qihoo notes.

The Chinese company also discovered that the botnet is using four different IPs for command and control (C&C), each serving a different purpose: downloader, controller, reporter, and loader. At the time of analysis, the researchers hadn’t seen a DDoS attack command issued, despite the necessary code to support such commands being present in the source file.

“The only instructions we saw are to download samples. This means the attacker is still focusing on spreading the botnets,” the researchers concluded.